Note: Crack from version 1.0.4.0 still works on this version, download it here:
 
https://www.piratebays.to/torrent/4979250/Grand_Theft_Auto_IV_v1.0.4.0_Update-RazorDOX-CrackOnly 

Patch 6 (1.0.6.0) Change log:

Rockstar Games Social Club

Remove Rockstar Games Social Club application 
Separate RGSC application no longer required to launch game 
Social Club login now occurs during the launch process 

Shadows 

A new, less memory-intensive, and better-looking scalable shadow solution has been implemented 
Enhanced Night Shadows added with user-selectable level of detail (replaces Shadow Density) 

Performance

Rendering optimizations have been made to improve performance, particularly when enabling shadows 
User-configurable graphics settings have been added for shadow control 
Improved memory management 
Multiplayer

Enhanced security to isolate users from cheaters and hackers 

Episodic Content

Provide in-game support to purchase "The Lost and Damned" and "The Ballad of Gay Tony" (Not available in Russian/Japanese Versions) 

Bug Fixes

Vehicle shadows re-enabled between 8pm and 6am 
Fix floating street textures 
Pedestrians in vehicles appear further out from the player to allow for long range sniping 
The Moon has been implemented with simulated lunar phases 
Fixed garbled text in Japanese Multiplayer menus 
"RESC 10" error fix for specific hardware configurations